The irony of using "Hiroshima bomb" as a unit of measurement

People love to use informal "units of measurement" to describe the magnitude of things, like "football fields", "Mount Everest" (both for height and volume) and, of course, perhaps the most famous of them all, "Hiroshima bombs".

That pseudo-unit of measurement has become so ubiquitous and so normalized that some even just call it "Hiroshimas" (eg. in YouTube videos), even though that makes no sense.

There's a huge irony in using that bomb as a unit of measurement, though.

And what's that irony? Well, all these informal units are used to give people a good mental picture of the size of something. When you say that the area of something is "ten football fields", that gives a decent mental picture because most people have an understanding of how large a football field is. If you say "two olympic swimming pools (in volume)", most people have at least a ballpark mental picture of how large that is.

But what exactly is the mental picture of the energetic power of the bomb dropped on Hiroshima?

The vast, vast majority of people have absolutely no idea. How big of an explosion was it? How much destruction did it cause? What was the blast radius? How far from the point of detonation did it cause significant damage to buildings?

The fact is that the vast, vast majority of people have absolutely no idea! Ask anybody any of those questions, and they will not know (some of them might throw wild guesses, but they will be just that, wild guesses and nothing more.)

That's because we don't have everyday experience with it, nor even have seen pretty much anything about it. There are some photos of the mushroom cloud (from which you can't even really see how large it is because there's no point of comparison), and stories about the destruction, but that's it. It's all extremely vague. 

So, quite ironically, this informal pseudo-unit of measurement, designed to give people a mental picture of the magnitude of something, is an extremely poor example of doing that. Even if you say "ten Hiroshima bombs" people will still have absolutely no idea how much that is. (Many people might get the impression that they do, but that's just an illusion. They actually don't, because they have no knowledge whatsoever about that magnitude, at any level. And usually they realize if they really start thinking about it.) 

That's quite different from something like "football field", where most people actually have some good mental picture of how large it is.